Author
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Lawton Jr, John |
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Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 5/5/2006 Publication Date: 10/1/2006 Citation: Lawton Jr, J.W. 2006. Isolation of zein using 100% ethanol. Cereal Chemistry. 83(5):565-568. Interpretive Summary: Zein is a group of proteins found in the endosperm of corn. These corn proteins are now accumulating because of the increase production of fuel ethanol from corn surpluses. Zein once had many industrial uses, but these uses were mostly lost to synthetic polymers. To recover some of these markets and reduce the surplus of corn protein, the price of zein must be reduced. Traditionally, zein is isolated and recovered from corn using aqueous alcohol as the solvent. It was found that zein can be recovered from corn using 100% ethanol at temperatures from 90 to 130 deg C. At these temperatures the zein precipitates from the ethanol once the temperature is lowered. By using only ethanol as the solvent and allowing the zein to precipitate, the recovery of zein from the solvent is easier than traditional zein isolation where the zein remains in the solvent at room temperature. The high temperature extraction method using 100% ethanol produced dried zein that averaged about 93% protein with no other purification steps, which is as pure as commercial zein. This extraction method will help the economics of fuel ethanol by producing a co-product that has industrial applications at cost than can compete with synthetic polymers. Technical Abstract: Traditionally, zein is isolated and recovered from corn gluten meal using aqueous alcohol as the solvent. Recovery of zein from this solvent is inconvenient and costly. Zein is insoluble in 100% ethanol at room temperature, but is soluble at 120 deg C in ethanol. Absolute ethanol was shown to effectively extract zein from corn gluten meal (CGM), distillers dried grains (DDG), and ground corn. Zein was extracted from CGM with absolute ethanol in a high pressure reactor at 130 deg C. After extracting at 130 deg C for 45 min., the solution was pumped out of the extractor and allowed to cool. Upon cooling the zein precipitated from solution. The precipitate was removed from the solution and air dried, resulting in 14% recovery of the starting material. The recovered precipitate had an average protein content of over 90% on a dry basis and accounted for about 22% of the CGM protein. The extraction did leave solids in the solvent phase which were recovered after the ethanol was evaporated. Surprisingly, these solids contained a high amount of protein. The recovered protein appeared to be zein upon SDS-PAGE analysis. It is not known why all of the zein did not precipitate after cooling. No differences were seen in the amount of zein extracted from CGM samples that were hand collected off the dewatering screen and gently dried, versus commercial CGM samples. The commercial CGM did produce a greater amount of solubles. The extraction procedure was also shown to work at temperatures as low as 90 deg C. The lower temperature did produce lower yields of extracted zein. The zein extracted at the lower temperatures was less brown, but zein extracted at either temperature was almost fully soluble in traditional zein solvents. |
